A bolt loosening test machine can be used to research looseness under the condition that a bolt bears the load, and the current bolt loading loosening test machines are classified into the following categories:
1 Junker Type Looseness Test Method
For example, GB/T 10431-2008. A Junker type looseness testing machine primarily applies an alternating transverse load to a fastener that applies a pretightening force to enable the fastener to move transversely. This transverse motion causes relative swing between a bolt and a nut, thereby resulting in greater micro slip of contact surface between threads and rapid looseness of the fastener. This allows the fastener to loosen faster than any previous test method.
2 Electro-Hydraulic Servo-Controlled Vibration Method
During test, a tested fastener is tightened on a clamping platform, and a specified pretightening force is produced. An alternating transverse displacement is produced between two clamped metal plates through a servo hydraulic cylinder, resulting in reduction or even loss of a clamping force. The instantaneous clamping forces are continuously recorded, and the anti-looseness properties of the fastener are judged by comparison.
3 NAS Vibration Test Method
A specimen is tightened into a test sleeve, and location marks are made on a part and the sleeve. Then, the sleeve is placed on a vibration testbed for moving back and forth. After starting, the sleeve impacts both ends of a guide back and forth in the guide, producing a large impact force and causing looseness of the specimen. During the test, the position change of the specimen is recorded with regular stop, and the anti-looseness properties of the specimen are judged accordingly.
All of the above test stations are intended for a single bolt loosening testbed, and bear single load. However, in the analysis of multi-bolt structures such as flanges, the load on the bolt cannot be simply and accurately equivalent to the single bolt due to the existence of the interaction between the bolts; and in the process of actual use of the bolts, in the case of a plurality of bolts, the load is generally complicated, and is not a single transverse load. Therefore, this testbed is designed to effectively simulate the actual load condition of the multi-bolt flange and to obtain the looseness of each bolt more appropriately when a plurality of bolts bear the load. At present, there is no relevant patent in the multi-bolt loosening test machine.